What I heard is that UnionFS is now working and several enhancements from Knoppix based distributions like Kantonix, Quantian, Paipix, Freeduc ... flowed back into Release 4.0. For example some Hardware support for widely used ISDN and DSL-Hardware from AVM, a enhanced Harddisk-Installer, and so on.
The DVD-Version is also directly bootable into the software-distributionsystem "m23". They also brought two e-books on it ("Knowing Knoppix" in english and "Knoppix Kompakt" in german). Also if you wish to choose between 4 different offices (OO 2.0 Beta(Build 104), KOffice, Abiword and Gnumeric), you should use Knoppix 4
So I think you can wait for the next version if you know something else to do while waiting on it...